Training weapon systems for recoilless antitank rifles of said type are already known. The training systems are designed to allow practice firing under the most realistic training conditions possible without the need to fire full-calibre rounds.
The training systems are based on the principle of arranging or incorporating a sub-calibre barrel or a so-called adapter insert into the barrel of the recoilless antitank rifle weapon for firing projectiles of smaller calibre than the live weapon.
A training weapon system of said type has been developed for the Carl Gustav antitank rifle and is based on a 20-mm calibre adapter system. The training weapon system described in the patent specification SE 511197 is designed for the absence of any recoil, which means that the training weapon generates a backblast effect comparable to that generated by the full-calibre weapon. The 20 mm calibre is entirely adequate for producing realistic sound levels of approximately 170 dB in practice firing, compared to approximately 180 dB in the case of full-calibre firing.
The adapter system comprises a barrel for sub-calibre projectiles fitted in a shell-like body, externally similar to 84 mm CG ammunition. The barrel is fitted in the shell-like body with a front guide for centring the barrel and a breech comprising a firing channel for a firing device and a nozzle screw thread for fitting a nozzle screw.
After loading the training weapon with 20 mm ammunition, attaching a firing device, fitting the nozzle screw and closing the end piece of the weapon, practice firing can be commenced.
One problem with said training weapons is that with repeated firing the nozzle screw thread is affected by leaking hot propellant gases, which expand under high pressure in the combustion chamber of the weapon, with the result that the gases not only erode the nozzle screw thread, thereby reducing its solidity, but also erode the nozzle aperture of the nozzle screw, which affects the performance of the weapon.
After an unknown number of firings the solidity in the nozzle thread will have been reduced to a level at which there is a risk of the nozzle screw becoming detached and expelled backwards through the nozzle aperture of the end piece as a projectile, which constitutes a risk to persons in the surrounding area. The service life of the nozzle screw depends on the number of rounds fired and can be difficult to estimate. Visual inspection, interpretation of the threads and the nozzle aperture, involves some uncertainty and does not eliminate the risk that the nozzle screw may fly off in the event of a fracture in the threaded fastening of the nozzle screw. If several different types of ammunition with different chamber pressures are incorporated into 20 mm training systems, it may be difficult to assess the service life in terms of the number of rounds.
In order to prevent the erosive effect of the gases on the threaded fastening and thereby to eliminate the risk of thread fracture, a ventilation hole has been made in the circumferential surface of the breech, in order to vent the propellant gases.
However, the ventilation hole has proved inadequate for venting the propellant gases, partly due to the fact that the hole cannot be made large enough, since too large a hole has a detrimental effect on the performance of the weapon, and partly due to the fact that solid products of combustion soon clog up the hole, thereby entirely preventing any ventilation.
Another problem that has been observed with said training weapons is that the training weapon can be fired without the nozzle screw having been fitted in the breech.
Firing with the training weapon without the nozzle screw fitted means that the ammunition, when fired, will stick in the barrel, so that excessive back-pressure is formed, which causes the base plate of the ammunition to splinter and fly backwards through the nozzle opening of the end piece. Loose flying splinters behind the training weapon constitute a risk to persons in the surrounding area.